In the decades after gold was discovered in California, lynch mobs hanged more than 300 people — frontier justice delivered by vigilantes. That part of the state’s history had faded until Scripps College art professor and photographer Ken Gonzales-Day found a picture one day. That led to another photograph and another, and now to an exhibit at the Vincent Price Museum of Art in Monterey Park.

“Originally, I was gonna write a book on images of Latinos from 1850 to 1900 portraiture,” said Gonzales-Day.

Speaking at the opening of the “Disappearing Into the Trees” exhibit, Gonzales-Day said one of the very first images he found was of a dapper Latino man in his early 20s.

“In a three-piece corduroy suit, leaning on a bearskin rug, in downtown Los Angeles,” explained the photographer. "And I thought it was a classic image that should be in any sort of history of photography."

Then he flipped the picture over, where something was written.

“'The last man hanged in Los Angeles.’ And it was that point I realized that I didn’t really understand what that meant.”

What it meant for Gonzales-Day was the start of a years-long odyssey across California in search of an untold story about mob justice and the more than 350 victims, most of them Latino, who’d vanished from history — far more than the number ever documented by another institution. "Seven times the known number than any other publication, or other person, knows about on this planet, except for me."

In most cases, the victims had committed or were accused of assault, rape or murder.

“Many of these victims were new immigrants, they were the new generation,” said Gonzales-Day, “people that were running up in precarious situations, and not always making the right choices. Some might go through the legal system, others might be summarily executed or hanged by a mob.”

These lynchings were often documented by professional photographers who’d create macabre souvenir postcards for the crowds of onlookers.

"[The photographers] would go out and shoot the body while it was still hanging either that night, or the first light of day," said Gonzales-Day. "Initially, they were sold as view cards and, once postcards were invented, then they would actually be made sometimes on the spot and sold to the mobs, because the mobs would be up to 3- to 4,000 people."

Gonzales-Day tracked down dozens of these images. For the exhibit, they’re blown up into the size of street murals, plunging the viewer into the scene. In one, a few men pose below the branches of a hanging tree. Some smile.

In others there’s a carnival-like setting; couples dressed in three-piece suits and mink stoles. Public hangings were often done at night, just as movie houses and bars were letting out.

Not seen are the victims. Gonzales-Day digitally removed them, “as a way of highlighting the historical erasure of Latinos from the history of lynching in the United States,” explained Gonzales-Day.

“And also to open up a sort of a metaphorical space in which you can contemplate the act. You can see the jeering crowd, you can see the lynchers pulling on the rope sort of in pantomime,” he said.

Gonzales-Day has spent much of the past decade trying to pull the victims and the perpetrators back into view. On a recent afternoon, he ushered a few dozen visitors through the exhibit.

“Wrestling with all those kind of stories, at some point realized I had to go,” he said. “I was reading on a case and I realized it was nearby, and I just said, you know, I’m just going to go get in the car and go look.”

And off he’d go, visiting actual lynching sites, or as close to them as he could find, from rural outposts in the Sierra foothills to big cities like L.A. (where Gonzales-Day has created a self-guided walking tour of lynching sites) to San Jose.

If people know of just one public hanging in California, it’s probably that of Tom Thurmond and Jack Holmes — lynched 80 years ago in a downtown San Jose park after allegedly murdering the son of a prominent businessman.

Newsreel footage from the time described the scene.

1933 San Jose St. James Park lynching newsreel report:

“Out into beautiful St. James Park, the pair was dragged, and on that tree, Thomas Thurmond was hanged to his doom in less time than it takes to tell it. Then his body was cut down and burned.”

Clip from the 1936 Spencer Tracy film “Fury” inspired by the hangings at San Jose’s St. James Park:

The killings got widespread attention; not only because they happened in a big city, but because Gov. James Rolph defended the mob in a radio and newsreel address.

“They were so aroused at the kidnapping and murdering of this young man,” said Rolph, "that they momentarily forgot themselves, and determined to give notice to the world that kidnapping and the murders which followed it, would not be tolerated in this state.”

Gonzales-Day said that you couldn't argue at that point it was still a frontier town. "I mean, in 1930 you know, people are taking jets, and having cocktails, and Hollywood is going, and there’s a lot of things that are not really terribly frontier-sy about the town by that point."

The last documented public lynchings in California happened just over 60 years ago. There are few if any markers or memorials. But Gonzales-Day said there are the trees.

“Disappearing Into the Trees” includes haunting portraits that he took of some of them, using an antique wooden field camera similar to the kind used by photographers of public lynchings.

“The majority of trees they used were the California native oak tree,” said Gonzales-Day, "which is interesting, because when you’re looking at all the possible trees in California, the California native oaks are not as common. People don’t really plant them so much anymore because they take a long time to grow, and they grow very slowly.”

Just as it's taken photographer Gonzales-Day a long time to unearth the story of California’s hanging trees and the many victims who bowed their branches.

“Disappearing into the Trees” is on view at the Vincent Price Museum of Art though April. Gonzales-Day’s book “Lynching in the West: 1850–1935” is available through Duke University Press Books.